In the typical elevator, hall call buttons, button lamps and lanterns are connected by many wires to an operational controller, which is usually located in the machine room, usually at the top of the building, in the basement, or on the first floor in a hydraulic elevator. The operational controller is linked to the elevator car by a traveling cable, and this cable, which dangles below the car, contains a great number of wires over which information is communicated between the car and the operational controller concerning car calls and other car operations, such as door opening functions. As a result, the amount of wire is quite extensive, and any reduction can provide significant cost savings. Moreover, a reduction in the size of the traveling cable will reduce the load, reducing power consumption. In fact, one reason the operational controller is not located in the car is to limit the weight of the traveling cable.
Telemetry techniques, using lasers, microwaves or nondirectional RF, theoretically could be used in an elevator to communicate this information, but this is not as easy as it may seem. An elevator is a comparatively hostile environment for data transmission, containing moving metallic parts, such as wires, rails and cables, which would cause interference, and considerable dust and dirt, which could interfere with optical systems. There is also a lot of RFI (radio frequency interference) from sources in the building because the hoistway is not shielded. Perhaps at considerable expense these problems could be overcome, but certainly not without increasing substantially the complexity of the equipment, making it far more difficult to service. Furthermore, these approaches may actually introduce into the building RFI that could interfere with other equipment, such as computers. Even with a telemetry system, a certain amount of hard-wiring would be required to provide redundancy and meet safety requirements. In short, telemetry approaches for elevators are appealing, but not practical.
Nevertheless, major advantages can be obtained by reducing the amount of wire in the system and the weight of the elevator car, by reducing the size of the traveling cable and the other wires in the system over which information is transferred. Moreover, if it were possible to locate the operational controller in the car, but without increasing the car's size or weight, less space would be required in the machine room, and even less wire would be needed in the system, especially in the traveling cable.